A recent study demonstrated that cancer cell growth is significantly suppressed by a reduction or loss of KMT5A-mediated methylation of proliferation cell nuclear antigen (PCNA), a widely recognized cell proliferation marker of tumor progression including that of parathyroid adenoma [35], suggesting that KMT5A-dependent PCNA methylation might promote the development of parathyroid adenoma. This evidence concerns the gene PCNA and cancer.